In commercial superheterodyne receivers, the local oscillator, after having been manually tuned to a frequency which converts a received signal to a predetermined i.f. frequency, is maintained tuned by means of an a.f.c. circuit. The latter derives an a.f.c. voltage at the frequency discriminator of the receiver, and applies that voltage to an electronic tuner, such as a voltage sensitive capacitor, connected in tuning relation to the local oscillator of the receiver. The problem is then faced that, after the a.f.c. circuit has locked the receiver to a carrier signal, it tends to hold the tuning when the local oscillator frequency is manually detuned, in opposition to the manually detuning, and thereby renders tuning to an adjacent carrier difficult. It is an object of the present invention to provide a control circuit for disabling the a.f.c. circuit of a superheterodyne receiver whenever the a.f.c. voltage of the receiver exceeds a predetermined level, indicative of manual detuning, and to employ parts of that control circuit for disabling the a.f.c. circuit in response to inter-channel noise. Thereby, a relatively slight movement of the tuning dial effects disablement of the a.f.c. circuit, and that disablement continues between channels. The a.f.c. circuit becomes again effective only when manual tuning has provided nearly precise capture of a second carrier signal.